William I (c. 1028 – 9 September 1087), usually known as William the Conqueror and sometimes William the Bastard, was the first Norman King of England, reigning from 1066 until his death in 1087. He was born in Falaise, Normandy, France. He launched the Norman conquest of England. The rest of his life was marked by struggles to consolidate his hold over England and his continental lands and by difficulties with his eldest son.

William was the son of the unmarried Robert I, Duke of Normandy, by Robert's mistress Herleva. His illegitimate status and his youth caused some difficulties for him after he succeeded his father, as did the anarchy that plagued the first years of his rule.

During his childhood and adolescence, members of the Norman aristocracy battled each other, both for control of the child duke and for their own ends. In 1047 William was able to quash a rebellion and begin to establish his authority over the duchy, a process that was not complete until about 1060.

In the 1050s and early 1060s, William became a contender for the throne of England, then held by the childless Edward the Confessor, his first cousin once removed. His reign in England was marked by the construction of castles, the settling of a new Norman nobility on the land, and change in the composition of the English clergy. He did not try to integrate his various domains into one empire but instead continued to administer each part separately.

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